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  Porous electroconductive material and process for production thereof; electrode and process for production thereof; fuel cell and process for production thereof; and electronic instrument, mobile machine, electric power generating system, cogeneration sysUSPTO Application #: 20070062821Title: Porous electroconductive material and process for production thereof; electrode and process for production thereof; fuel cell and process for production thereof; and electronic instrument, mobile machine, electric power generating system, cogeneration sys Abstract: A porous electroconductive material is provided. The electroconductive material enables efficient enzymatic metabolic reactions on electrodes and yields electrodes having immobilized enzymes thereon which remain stable in any working environment. The porous electroconductive material, which has a three-dimensional network structure, is formed from a skeleton of porous material and a carbonaceous material covering the surface of the skeleton. The porous material constituting the skeleton is foamed metal or alloy. This porous electroconductive material is made into an electrode, and enzymes are immobilized on this electrode. The resulting electrode with immobilized enzymes thereon is used as the anode of a bio-fuel cell. (end of abstract) Agent: Bell, Boyd & Lloyd, LLP - Chicago, IL, US Inventors: Atsushi Sato, Hideki Sakai, Mamoru Hatakeyama, Takaaki Nakagawa USPTO Applicaton #: 20070062821 - Class: 205777500 (USPTO) Related Patent Categories: Electrolysis: Processes, Compositions Used Therein, And Methods Of Preparing The Compositions, Electrolytic Analysis Or Testing (process And Electrolyte Composition), Involving Enzyme Or Micro-organism The Patent Description & Claims data below is from USPTO Patent Application 20070062821. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCES TO RELATED APPLICATIONS [0001] The present application claims priority to Japanese Patent Application JP 2005-216808 filed in the Japanese Patent Office on Jul. 27, 2005, the entire contents of which being incorporated herein by reference. BACKGROUND [0002] Metabolism in a living body is an extremely efficient reaction with a high substrate specificity which proceeds in a comparatively mild environment (neutral at room temperature). Such metabolism includes respiration and photosynthesis that converts nutrients (such as oxygen, saccharides, fats, and proteins) into energy required for growth of microbes and cells. [0003] Biocatalysts (or enzymes) composed of proteins get deeply involved in such reactions in a living body. The idea of utilizing the catalytic action of enzymes had been put to practice in the long human history. The application of enzymes covers various fields such as brewing industry, fermentation industry, textile industry, leather industry, food industry, and pharmaceutical industry. Enzymes are expected to find new uses in the field of electronics, such as biosensors, bioreactors, and bio-fuel cells, which have electrodes catalyzed by enzymes. [0004] Unfortunately, enzymes have been used exclusively in an aqueous medium because they are proteins which are unstable to heat, strong acid and alkali, and organic solvent. In the past, the enzymatic reaction has been carried out by the batchwise process that causes enzymes dissolved in an aqueous medium to react on the substrate. The batchwise process is uneconomical because it is repeated after enzymes have been discarded. In fact, it is very difficult to recover enzymes intact (for reuse) from reaction solutions. [0005] To address this problem, there have been proposed immobilized enzymes, which are insoluble in water. Immobilized enzymes (with high substrate specificity) can be used in the same way as solid catalysts for ordinary chemical reactions. Immobilization is a highly effective way of using enzymes. [0006] The same is true for the application of enzymes to electrodes. Enzymes densely immobilized on the surface of an electrode produce enzymatic reactions near the electrode and such enzymatic reactions can be detected as electric signals. Incidentally, an electron mediator (or electron acceptor) is necessary between the enzyme (protein) and the electrode to promote electron transfer, and this electron mediator should also be immobilized preferably. [0007] There are generally two methods for immobilizing enzymes on electrodes--the entrapping method and the bonding method. Research is progressing on how to immobilize enzymes on various electrode materials. [0008] According to the related arts, electrode materials which have preferentially been used for high reaction efficiency are carbonaceous porous ones with a large surface area. (See, Japanese Patent Laid-open Publication (JP-A) No. 2000-133297, JP-A No. 2003-282124, JP-A No. 2004-71559 and JP-A No. 2005-13210.) Carbonaceous porous electrode materials, however, have a very small pore diameter and are limited in porosity (which affects strength). Consequently, they prevent a solution (containing enzymes or substrate for reactions) from infiltrating into them, resulting in uneven distribution of enzymes and substrate. That is, the advantage of their high surface area has not been fully utilized. This problem is more serious when a highly viscous solution is used or the enzymatic reactions involve a large pH change. In these cases, the solution does not infiltrate into the inside and the buffering function does not follow the abrupt pH change in the electrode, which would lead to enzyme deactivation. [0009] Much has been studied about immobilization of enzymes on carbonaceous materials as well as metallic materials such as titanium, copper, aluminum, nickel, stainless steel, chromium, gold, and platinum. (See, Japanese Patent Laid-open Publication (JP-A) No. 2000-133297, JP-A No. 2003-282124 and JP-A No. 2004-71559.) However, metallic materials are poor in stability (or liable to corrosion and dissolution depending on solution pH and potential) and inferior in surface area to carbonaceous materials. [0010] Although carbonaceous materials as well as, metallic materials have been used as raw materials for electrodes on which enzymes are to be immobilized, they have their merits and demerits, as mentioned above. [0011] It is desirable to provide a porous electroconductive material and a process for production thereof; an electrode made of the electroconductive material and a process for production thereof; a highly efficient fuel call equipped with the electrodes on which enzymes are immobilized and a process for production thereof; and an electrode reaction-based apparatus equipped with the electrodes having immobilized enzymes thereon the porous electroconductive material is characterized by adequate pore diameters (large enough for a solution containing the substrate to easily pass through), high porosity, high conductivity, and large surface areas. Moreover, the porous electroconductive material enables efficient enzymatic metabolic reactions on electrodes and yields electrodes having immobilized enzymes thereon which remain stable in any working environment. [0012] It is further desirable to provide an electronic instrument, a mobile machine, an electric power generating system, and a cogeneration system, which are equipped with the highly efficient fuel cell. SUMMARY [0013] The present application relates to a porous electroconductive material and a process for production thereof; an electrode and a process for production thereof; a fuel call and a process for production thereof; and an electronic instrument, a mobile machine, an electric power generating system, a cogeneration system, and an electrode reaction-based apparatus. More particularly, the present application will find use as a fuel cell that works with the help of enzymes and a variety of instruments, apparatuses, and systems that utilize this fuel cell as their power source. [0014] The first embodiment is directed to a porous electroconductive material which includes a skeleton of porous material and a material composed mainly of carbonaceous material which covers at least part of the skeleton. [0015] The second embodiment is directed to a process for producing a porous electroconductive material, the process comprising a step of coating the surface of a skeleton of porous material at least partly with a material composed mainly of carbonaceous material. [0016] In the first and second embodiments, the porous material constituting the skeleton of the porous electroconductive material is not restricted (particularly in conductivity) so long as it has high porosity and is capable of stably maintaining the skeleton. The porous electroconductive material to be used as the electrode on which enzymes are to be immobilized should preferably have high porosity and high conductivity. Such porous materials (with high porosity and high conductivity) includes, for example, metallic materials (metals and alloys) and carbonaceous materials (with reinforced skeletons). Metallic materials as the porous materials may be selected from among many candidates such as nickel, copper, silver, gold, nickel-chrome alloy, and stainless steel (in the form of foamed metal or alloy). Selection depends on the solution pH and potential that vary according to the environment in which they are used. Porous materials (in addition to the above-mentioned metallic and carbonaceous materials) include spongy resinous materials. These porous materials should have adequate porosity and pore diameter (or minimum pore diameter) which are determined by the thickness of the carbonaceous material to be applied to the skeletons of the porous material and also by the porosity and pore diameter required of the porous electroconductive material. The pore diameter of the porous material is usually 10 nm to 1 mm, typically 10 nm to 600 .quadrature.m. [0017] On the other hand, the material that covers the skeleton is not specifically restricted so long as it has electroconductivity. The porous electroconductive material that is used as electrodes (particularly those on which enzymes are immobilized) should have adequate electroconductivity and stability at the expected potential. Such materials are selected from those which are composed mainly of carbonaceous materials. The carbonaceous materials are usually have a wide potential window and are chemically stable. The material composed mainly of carbonaceous material may be one which is composed solely of carbonaceous material or one which is composed mainly of carbonaceous material and a small amount of secondary material which is selected according to the characteristic properties required of the porous electroconductive material. Examples of the second material include carbonaceous materials incorporated with a highly electroconductive material (such as metal) which enhances electroconductivity and carbonaceous materials incorporated with polytetrafluoroethylene which imparts water repellency (other than electroconductivity). The carbonaceous materials are not specifically restricted; they may be carbon in the form of simple substance or a mixture of carbon with other elements. The carbonaceous material should preferably be in the form of fine powder having large surface areas and high electroconductivity. Examples of such carbonaceous materials include Ketjenblack (with high electroconductivity) and functional carbonaceous materials (such as carbon nanotube and fullerene). The material composed mainly of carbonaceous material may be applied to the skeleton of the porous material by any method using an adequate adhesive. The coating method is not specifically restricted. [0018] The porous electroconductive material that is used for the electrode on which enzymes are to be immobilized should have an adequate pore diameter that permits easy passage of solutions containing the substrate. The pore diameter should be 9 nm to 1 mm, preferably 1 .quadrature.m to 1 mm, more preferably 1 .quadrature.m to 600 .quadrature.m. [0019] The partial coating of the skeleton of porous material with the material composed mainly of carbonaceous material should preferably be carried out such that pores communicate with one another, without the coating material clogging pores. [0020] A third embodiment is directed to an electrode of porous electroconductive material comprising a skeleton of porous material and a material composed mainly of carbonaceous material which covers at least part of the skeleton. [0021] A fourth embodiment is directed to a process for producing an electrode, the process comprising coating the surface of a skeleton of porous material at least partly with a material composed mainly of carbonaceous material, thereby forming a porous electroconductive material, and molding the porous electroconductive material into an electrode. Continue reading... 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